Use of propyl propane thiosulfinate and propyl propane thiosulfonate for the prevention and reduction of parasites in aquatic animals

ABSTRACT

A method for reducing parasites in aquatic animals is provided. The method includes administering to the aquatic animal a compound comprising propyl propane thiosulfonate (PTSO) having the formula R—SOa-S—R, where R represents n-propyl group (—CH 2 —CH 2 —CH 3 ) and a is 2 and also propyl propane thiosulfinate (PTS) having the formula R—SOa-S—R, where R represents n-propyl group (—CH 2 —CH 2 —CH 3 ) and a is 1, so that a combination of PTS and PTSO is administered to the aquatic animal resulting in the reduction of a plurality of crustaceans infecting the aquatic animal in response to administering the combination of PTS and PTSO to the aquatic animal.

CROSS-REFERENCE OF RELATED APPLICATIONS

This application is a Continuation-in-Part of U.S. patent applicationSer. No. 14/043,160, filed on Oct. 1, 2013, now U.S. Pat. No. 9,271,947,which is incorporated herein by reference in its entirety. Thisapplication is related to European Patent Application No. EP13186923.2,filed Oct. 1, 2013, and also Patent Cooperation Treaty Application No.PCT/IB2014/002548, filed on Sep. 30, 2014, both are also incorporatedherein by reference in their entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to aquaculture and, more particularly, tothe prevention and reduction of parasites in aquatic animals.

Description of the Related Art

Aquaculture, also known as fish or shellfish farming, refers to thebreeding, rearing, and harvesting of plants and animals in all types ofwater environments, including ponds, rivers, lakes, and oceans. Issuesassociated with aquaculture can include the propagation of invasivespecies, waste handling, side-effects of antibiotics, and competitionbetween farmed and wild animals. In addition, the welfare of the animalsin aquaculture can be impacted by stocking densities, behavioralinteractions, diseases, and parasitosis.

Fish may be infected with numerous parasites belonging to variouszoological groups. The most common types of infestation are caused byprotozoans, like dinoflagellates ectoparasites, ciliates, andzooflagellates. Another species of interest in aquaculture isrepresented by helminth parasites, such as monogeneans, trematodes,cestodes and nematodes. In addition, parasites affecting aquaculturealso include ectoparasites, such as mollusks, crustaceans, and sea lice.

The conventional strategies for controlling parasites and the resultinginfections are expensive since they are based on chemoprophylaxis.Furthermore, the hardening of the regulations and the banning of the useof certain drugs, such as malachite green and gentian violet, againstparasites in farms requires new approaches and strategies for parasitedisease control.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention address deficiencies of the art inrespect to the prevention and reduction of parasites in aquatic animalsand provide a novel and non-obvious method for reducing parasites inaquatic animals. In an embodiment of the invention, propyl propanethiosulfinate (PTS) having the formula R—SOa-S—R, where R representsn-propyl group (—CH₂—CH₂—CH₃) and a is 1, can be administered to aquaticanimals including fish, crustaceans, and molluscs, to reduce multiple,different parasites, including crustaceans, in the aquatic animals.Further, the concentration of PTS can be between at least one and nomore than five thousand parts per million (1-5000 ppm).

In a different embodiment of the invention, propyl propane thiosulfonate(PTSO) having the formula R—SOa-S—R, where R represents n-propyl group(—CH₂—CH₂—CH₃) and a is 2, can be administered to an aquatic animal toreduce multiple, different parasites, such as crustaceans, in theaquatic animal. Further, the concentration of PTSO can be between atleast one and no more than five thousand parts per million (1-5000 ppm).

In yet a different embodiment of the invention, a compound includingboth propyl propane thiosulfonate (PTSO) having a formula R—SOa-S—R,where R represents n-propyl group (—CH₂—CH₂—CH₃) and a is 2, and alsopropyl propane thiosulfinate (PTS) having a formula R—SOa-S—R, where Rrepresents n-propyl group (—CH₂—CH₂—CH₃) and a is 1, can be administeredto a aquatic animal to reduce multiple, different parasites, such ascrustaceans, in the aquatic animal.

In even yet a different embodiment of the invention, a compoundincluding both propyl propane thiosulfonate (PTSO) having a formulaR—SOa-S—R, where R represents n-propyl group (—CH₂—CH₂—CH₃) and a is 2,and also propyl propane thiosulfinate (PTS) having a formula R—SOa-S—R,where R represents n-propyl group (—CH₂—CH₂—CH₃) and a is 1, can beadministered to a fish to prevent multiple, different parasites frominfecting the aquatic animal. In yet a different embodiment of theinvention, PTS can be administered to an aquatic animal to preventmultiple, different parasites from infecting the aquatic animal. Inanother embodiment, PTSO can be administered to an aquatic animal toprevent multiple, different parasites from infecting the aquatic animal.

Additional aspects of the invention will be set forth in part in thedescription which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The aspectsof the invention will be realized and attained by means of the elementsand combinations particularly pointed out in the appended claims. It isto be understood that both the foregoing general description and thefollowing detailed description are exemplary and explanatory only andare not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute partof this specification, illustrate embodiments of the invention andtogether with the description, serve to explain the principles of theinvention. The embodiments illustrated herein are presently preferred;it being understood, however, that the invention is not limited to theprecise arrangements and instrumentalities shown, wherein:

FIG. 1 is a pictorial illustration of a method for reducing parasites inaquatic animals;

FIG. 2A is a flow chart illustrating a method for reducing parasites inaquatic animals;

FIG. 2B is a flow chart illustrating a method for preventing parasitesin aquatic animals;

FIG. 3 illustrates the survival probability of Caligus rogercresseyicopepodites at different concentrations of PTS and PTSO;

FIG. 4 illustrates the survival probability of Caligus rogercresseyiNauplius I at different concentrations of PTS and PTSO;

FIG. 5 illustrates the survival probability of Caligus rogercresseyiNauplius II at different concentrations of PTS and PTSO;

FIG. 6 illustrates the survival probability of Caligus rogercresseyiadults at different concentrations of PTS and PTSO;

FIG. 7 illustrates assay effectiveness at different concentrations ofPTSO on the control of Icthyobodo necator in rainbow trout;

FIG. 8 illustrates in vitro activity of PTS, PTSO, and a mixture of both(1:1) against L3 larvae of Hysterotylacium aduncum at the concentrationtested (75 ppm), where activity is expressed as mortality; and,

FIG. 9 illustrates in vitro activity of PTSO against L3 larvae ofAnisakis type I at the concentrations tested (200, 300 and 500 ppm),where activity is expressed as mortality.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention provide for combating parasites in aquaticanimals, including fish, mollusks, and crustaceans. Specifically, propylpropane thiosulfonate (PTSO) and propyl propane thiosulfinate (PTS) canbe used alone or in combination with each other as an anti-parasiticagainst a variety of parasites, such as flagellate protozoan, helminths,mollusks, crustaceans, and bloodsuckers, in aquatic animals, such asfish, mollusks, and crustaceans, so that parasites invading fish,mollusk, and crustaceans can both be reduced as well as prevented.

In further illustration of the invention, FIG. 1 pictorially shows aprocess for reducing parasites in aquatic animals. Of note, in additionto reducing parasites in aquatic animals, it is contemplated that theinvention can also be used to eliminate parasites in aquatic animals.Upon the detection of a plurality of parasites on and/or in infectedaquatic animals 105, such as in and/or on fish 805A, crustaceans 805B,and mollusks 805C, propyl propane thiosulfonate (PTSO) 150B as well aspropyl propane thiosulfinate (PTS) 150A can be used alone or incombination with each other 150 to reduce the number of parasites inor/and on the aquatic animals 105.

More specifically, upon the detection of a parasite, PTS and/or PTSO 150can be administered 115 to an infected aquatic animal 105. Theadministration of PTS and/or PTSO 150 to an infected aquatic animal 105can be accomplished via an injection 115A, a bath treatment 115B,incorporation with a pharmacological composition and orally administered115C, incorporation with a pharmacological composition and injected115D, or incorporated with food and then orally administrated 115E. Inthis way, after the administration of PTS and/or PTSO 150, the parasitesin and/or on the infected aquatic animal 105 are reduced (and/oreliminated).

In yet further illustration of the invention, FIG. 2A is a flow chartillustrating a process for reducing parasites in aquatic animals.Beginning in block 212, an aquatic animal can be selected. The aquaticanimal can be a fish (a member of a paraphyltic group of organisms thatincludes gill-bearing aquatic craniate animals), a crustacean, or amollusk. The selected aquatic animal can be tested for the presence ofparasites whether on and/or in the selected aquatic animal, as shown inblock 222, by any method now known or later developed. Of note, testingcan also include the visual inspection of the aquatic animal. Asillustrated in block 232, upon the detection of a parasite, such asendoparasites and ectoparasites, including, but not limited to,flagellated protozoan, helminth, nematodes, trematodes, cestodes,bloodsuckers, copepods (such as sea lice), crustaceans, and mollusks, adetermination as to what to administer to the infected aquatic animalcan be made, as indicated in block 242. Of note, with reference to theparasite being a crustacean as well as a copepod, the parasite caninclude those having a scientific classification of Class Maxillopodaand Subclass copepod, which act as ectoparasites.

Specifically, a determination can be made as to whether PTS, PTSO, or acombination of both should be administered. In addition, as shown inblock 252, an optional determination as whether PTS, PTSO, or both canbe administered in conjunction with a pharmacological composition, suchas drugs and other anti-parasitic products, can be made. Further, adetermination can be made as to how to administer PTS, PTSO, or both, asshown in block 262. For instance, administration of PTS, PTSO, or bothcan be accomplished via an injection, a bath treatment, or incorporatedwith food and then orally administrated in the aquatic animal. Further,if a pharmacological composition is also selected to be added, then PTS,PTSO, or both can be incorporated with the pharmacological compositionand orally administered or incorporated with the pharmacologicalcomposition and injected.

In yet further illustration of the invention, FIG. 2B is a flow chartillustrating a process for preventing parasites in aquatic animals. Asillustrated in FIG. 2B, an aquatic animal can be selected, as shown inblock 218. As before, the aquatic animal can be a fish (a member of aparaphyltic group of organisms that includes gill-bearing aquaticcraniate animals), a crustacean, or a mollusk. Optionally, an aquaticanimal can be tested, by any method now known or later developed,including by visual inspection, to determining whether the selectedaquatic animal is infected by a parasite (or multiple, differentparasites), as illustrated in block 228. Regardless of whether it isdetermined that the selected aquatic animal is infected by parasites, asshown in block 248, a determination can be made as to what to administerto the selected aquatic animal—PTS, PTSO, both. In addition, as shown inblock 258, an optional determination as whether PTS, PTSO, or both canbe administered in conjunction with a pharmacological composition, suchas drugs and other anti-parasitic products, can be made.

Also, a determination can be made as to how to administer PTS, PTSO, orboth, as shown in block 268. For instance, administration of PTS, PTSO,or both can be accomplished via an injection, a bath treatment, orincorporated with food and then orally administrated to the aquaticanimal. Even yet further, if a pharmacological composition is alsoselected to be added, then PTS, PTSO, or both can be incorporated withthe pharmacological composition and orally administered or incorporatedwith the pharmacological composition and injected. In this way, PTS,PTSO, or both, can be used in the prevention of parasites in aquaticanimals.

Of note, as indicated herein the use of propyl propane thiosulfonate(PTSO) as well as propyl propane thiosulfinate (PTS) can be used aloneor in combination with each other. In other words, PTS and PTSO can beused alone or in combination with each other in any relative percentage(in any ratio). In addition, PTS and PTSO can be used in combinationwith other anti-parasitic methods and products, including naturalproducts or synthetic drugs, where PTS and/or PTSO can be in any ratio.The parasites can include endoparasites and ectoparasites, including,but are not limited to, flagellated protozoan, helminth, nematodes,trematodes, cestodes, bloodsuckers, copepods (such as sea lice),crustaceans, and mollusks. The aquatic animals being treated by PTSand/or PTSO can include, but are not limited to, fish (including freshwater and saline (marine) water species) such as salmon, trout, bass,seabream, fishbase, tilapia, turbot, cod, carp, sturgeon, flatfish, eel,tuna, catfish, coho, lobster, crab, mussel, clam, shrimp and prawn,mullet, shell, and oyster.

PTS and PTSO each correspond to the following formula:R—SOa-S—R,in which R represents n-propyl group (—CH₂—CH₂—CH₃), and a is 1 for PTSand 2 for PTSO. Of note, PTSO is also known as dipropyl thiosulfonate(CAS Number 1113-13-9) and PTS is also known as dipropyl thiosulfinate(CAS Number 1948-52-3). The concentration of PTS used in an embodimentof the invention to reduce a plurality of parasites in and/or on a fish(and also in crustaceans and mollusks) can be between one and fivethousand parts per million (1-5000 ppm). In a different embodiment, theconcentration of PTS can be between five and one thousand parts permillion (5-1000 ppm). In yet a different embodiment, the concentrationof PTS can be between ten and three hundred fifty parts per million(10-350 ppm).

In yet even a different embodiment, the concentration of PTS can bebetween 10 and four hundred parts per million (10-400 ppm). Theconcentration of PTSO used in an embodiment of the invention to reduce aplurality of parasites in fish (as well as on fish) can be between oneand five thousand parts per million (1-5000 ppm). In a differentembodiment, the concentration of PTSO compound can be between five andone thousand parts per million (5-1000 ppm). In yet a differentembodiment, the concentration of PTSO can be between ten and threehundred fifty parts per million (10-350 ppm). In yet even a differentembodiment, the concentration of PTSO can be between 10 and four hundredparts per million (10-400 ppm).

In addition, PTS and/or PTSO can be administered to a healthy aquaticanimal or an infected aquatic animal by an immersion treatment, such asa bath. In other words, PTS and/or PTSO can be used to reduce the numberof parasites in and/or on an aquatic animal as well as PTS and/or PTSOcan be used in the prevention of parasites in aquatic animals. Inaddition, PTS and/or PTSO can be incorporated into feed; the feed canthen be administered to either a healthy aquatic animal or an infectedaquatic animal. To that end, in a different embodiment, PTS and/or PTSOcan be administered orally. For example, PTS and/or PTSO can beincorporated into a pharmacological composition (including drugs andother anti-parasitic products) and then the pharmacological compositioncan be orally administered to the aquatic animal.

In another embodiment, PTS and/or PTSO can be incorporated into apharmacological composition (including drugs and other anti-parasiticproducts) and then the pharmacological composition can be injected intothe aquatic animal. In addition, PTS and/or PTSO can be administered toan aquatic animal directly by injection alone (with just PTS, just PTSO,or only a mixture of PTS and PTSO).

In further illustration of the invention, the following examples arepresented. Of note, as will be understood by one skilled in the art, theinvention is not limited to just these examples.

EXAMPLE 1

The parasiticide efficacy of a mixture of propyl propane thiosulfinate(PTS) and propyl propane thiosulfonate (PTSO) was measured in vitroagainst Caligus rogercresseyi.

Upon receipt in the laboratory, the wild adult females and males werekept in filtered seawater (125 μm membranes) in absolute darkness insidea thermo-regulated chamber at 12° C. The egg sacs were removed gentlyfrom females using a fine-tipped forceps and placed in separate beakerswith 500 mL of filtered seawater in the conditions described above untilspawning. The fish were then separated into the different stages:Nauplius I, Nauplius II, Copepodite and Adult for subsequent in vitrosusceptibility studies.

In order to evaluate effectiveness, several bioassays were performed intriplicate with different concentrations of propyl propane thiosulfinate(PTS) and propyl propane thiosulfonate (PTSO) at each stage: Nauplio I,Nauplio II, Copepodite and Adult. In total, 40 Caligus were used pertest and placed at a rate of 10 individuals per sterile petri plate. Amixture of propyl propane thiosulfinate (PTS) and propyl propanethiosulfonate (PTSO) at concentrations of 100, 200 and 300 ppm was addedto each plate over a 30-minute exposure period. After that, the waterwas changed and the fish were incubated at 12° C. during a 12-hourphotoperiod. A control group was also included. In order to estimate theeffective lethal concentration and the survival ratio, observations wereregistered after treatment using the Kaplan-Meir function for each ofthe stages and treatments studied.

EXAMPLE 2

In this example, a study of oral treatments of Ichthyobodosis in rainbowtrout with different concentrations of Propyl propane thiosulphonate(PTSO) administered into feed was conducted.

Rainbow trout Oncornynchus mykiss were obtained from a local fish farmand acclimatized for at least 10 days before assay in 100 l tanks withaeration in closed systems of water (15±2° C., pH 7-7.5). The naturallight-dark cycle was simulated (12 h light: 12 h dark). Fish were fedtwice per day with a commercial feed (EFICO, Biomar, Spain).Parasite-free fish were experimentally infested by holding theparasite-free fish 25 days in a 100 l tank that also contained fishshowing high-intensity infestation (20 uninfected fish to 10 infectedfish). Twenty (20) fish were then sampled at random for determination ofinfestation intensity, which was determined to be a high intensityinfestation in at least 50% of fish.

Fish were anaesthetized by immersion in bath with 100 ppm of Tricainemethanesulfonate until respiration became weak. A mucus sample was thentaken by gently scraping the body surface after examination of a samplearea of 24×32 mm. The sample was mixed with 30 μl of distilled water ona slide, cover-slipped and examined to optic microscopy (400×).

Each treatment was assayed in 20 infected fish maintained in 100 L tankswith aeration in closed systems of water. The fish received feedcontaining three different treatments. The first group received a dietwith 100 ppm of Propyl propane thiosulphonate (PTSO), the secondreceived a diet supplemented with 300 ppm of PTSO, and the thirdreceived a diet with 300 ppm of metronidazole. All treatments wereapplied during a 10 day period. In all cases, feed was supplied at 2% oftotal body weight per day. Simultaneously, a positive control assay(also on 20 infected fish treated identically, but without any PTSO) andnegative control assay (with 20 uninfected animals) were performed.Tanks conditions were identical to those during the acclimatizationperiod.

Throughout the assay period the fish were monitored regularly to ensurethat the fish were eating the food, and to check for signs of toxicity.

EXAMPLE 3

The objective of example 3 was to examine the activity of propyl propanethiosulphonate (PTSO) and propyl propane thiosulfinate (PTS) against L3larvae of type I Anisakis and Hysterotylacium aduncum to explore thepossible use of these compounds for prophylaxis treatments.

L3 of Anisakis type I and Hysterotylacium aduncum were collected bydissecting the fish Micromesistius poutassou (blue whiting) andTrachurus trachurus (mackerel) fished in the Cantabric sea, andselecting only larvae with a length greater than (>) 2.0 cm in the caseof Anisakis, and greater than 0.8 cm for Hysterotylacium.

Larvae were axenised in antibiotic solution (Iglesias et al., 1997),introduced into polystyrene plate wells with 2 ml of sterile solution of0.9% NaCl and the different concentrations of PTS alone, PTSO alone, andboth PTS and PTSO (75, 200, 300 and 500 ppm) and then incubated at 36°C. in a 5% CO₂ atmosphere. As controls, larvae were assayed without testcompound under identical experimental conditions, and using only thesolvent DMSO 1% (Dimethyl sulfoxide). Larvae were examined understereoscopic microscope at 4, 8, 24, and 48 hours to test the biocidaleffect of the compounds. Larvae with no mobility at all were considereddead. Each dilution was tested three times on larvae from fish capturedon different days.

EXAMPLE 4

One hundred fifty (150) parasitic copepods (Caligus rogercresseyi) werecollected from parasitized trout, which had been previously sedated withmethanesulfonate. The parasitic copepods were kept in water extractedfrom an aquaculture farm. For the experiment, thirty (30) adult trout(Onchorhynchus mykiss) were used and distributed in three (3) tanks(with ten (10) fish per tank), of three hundred liters (300 L) of waterin each tank with supplemental aeration, closed circuit and controlledphysico-chemical parameters.

In each tank, fifty (50) adult copepods were distributed and maintainedfor twenty four hours (24 h) in contact with the trout. After the twentyfour hours the adult copepods were removed. To assess the anti-parasiticeffect of a PTSO/PTS combination, at a total concentration of one partper million (1 ppm) with equal parts of MO and PTS, the trout whereexposed to the PTSO/PTS combination in a bath (in a different tank) forone hour (1 h), following the experimental model:

-   -   Tank 1: Control. Fish without treatment, exposed to a single        bath in fresh water without additives for one hour (1 h).    -   Tank 2: Fish exposed to a single bath with PTSO/PTS in equal        parts having a total concentration of one part per million (1        ppm) for one hour (1 h).    -   Tank 3: Fish treated in PTSO/PTS in equal parts having a total        concentration of one part per million (1 ppm) for one hour (1        h), repeating the treatment once a day for three (3) days.

After the treatments, the trout were returned to the tanks. After twentyfour hours (24 h), the load of copepods was measured, evaluating thesurvival and infection capacity of the copepods (sea lice). Resultsshowed that a reduction of the parasitic copepods viability on thetreated trout for those trout treated with a combination of PTSO/PTS.More specifically, for the trout in tank 3, there was only a twentypercent (20%) recover of the parasitic copepods on the trout and for thetrout in tank 2, there was a fifty seven percent (57%) recover of theparasitic copepods on the trout. However, for the trout in tank 1, therewas a one hundred percent (100%) recover of the parasitic copepods onthe trout. Of note, the recover and, in particular, the percent ofrecover, is based on a visual inspection of the trout's body, as wherethere are parasitic copepods present on the trout can be visuallydetermined. Further, the percent of recover is calculated by determiningthe number of fish showing signs of the presence of parasitic copepodsdivided by the total number of fish in the tank.

Exemplary Results

The administration of PTS and PTSO demonstrated anti-parasitic activityagainst stages of the life C. rogercresseyi. For example, FIG. 3illustrates the survival probability of Caligus rogercresseyicopepodites at different concentrations of PTS and PTSO.

In addition, FIG. 4 illustrates the survival probability of Caligusrogercresseyi Nauplius I at different concentrations of PTS and PTSO.

In further illustration of the exemplary results, FIG. 5 illustrates thesurvival probability of Caligus rogercresseyi Nauplius II at differentconcentrations of PTS and PTSO.

Finally, FIG. 6 illustrates the survival probability of Caligusrogercresseyi adults at different concentrations of PTS and PTSO.

It is further noted that PTSO demonstrated antiparasitic activityagainst Icthyobodo necator in rainbow trout with significant reductionof infestation intensity as shown in Table 1. For each treatment andeach dosage tested, infestation intensity 24 hours after the end of theassay is shown for each of the 20 fish included in each assay. Alsoshown is infestation intensity: high, moderate, low, minimal and zero(i.e. no Icthyobodo necator detected in body scrapings).

TABLE 1 % infestation High Moderate Low minimal zero Positive control 5341 6 0 0 PTSO (100 ppm) 35 30 18 12 5 PTSO (300 ppm) 25 7 8 5 55Metronidazole (300 ppm) 15 20 7 12 46

Of note, infestation intensity was based on a 5-point scale, as follows:Zero equals Ichthyobodo necator not being detected in the sample;Minimal equals only 1 individual of I. necator being detected in thesample; Low equals more than 1 individual of parasite being detected inthe sample, the average number per microscope field being less than 10;Moderate equals an average number of individuals per microscope field of10 to 50; High equals an average number of individuals per microscopefield of more than 50.

Further, FIG. 7 illustrates assay effectiveness at differentconcentrations of PTSO on the control of Icthyobodo necator in rainbowtrout.

In addition, PTS and PTSO demonstrated significant anti-parasiticactivity against L3 larvae of Hysterotylacium aduncum and Anisakis typeI, as shown in FIG. 8.

Specifically, FIG. 8 illustrates in vitro activity of PTS, PTSO, and amixture of both (1:1) against L3 larvae of Hysterotylacium aduncum atthe concentration tested (75 ppm), where activity is expressed asmortality. In addition, in FIG. 9, in vitro activity of PTSO against L3larvae of Anisakis type I at the concentrations tested (200, 300 and 500ppm), where activity is expressed as mortality is illustrated.

Having thus described the invention of the present application in detailand by reference to embodiments thereof, it will be apparent thatmodifications and variations are possible without departing from thescope of the invention defined in the appended claims as follows:

We claim:
 1. A method for reducing parasites in aquatic animals,comprising: administering to an aquatic animal propyl propanethiosulfinate (PTS), the PTS having a formula R—SOa-S—R, where Rrepresents n-propyl group (—CH₂—CH₂—CH₃) and a is 1 and alsoadministering propyl propane thiosulfonate (PTSO), the PTSO having aformula R—SOa-S—R, where R represents n-propyl group (—CH₂—CH₂—CH₃) anda is 2, so that a combination of PTS and PTSO is administered to theaquatic animal, whereby reducing a plurality of crustaceans infectingthe aquatic animal in response to administering the combination of PTSand PTSO to the aquatic animal.
 2. The method of claim 1, wherein thecombination of PTS and PTSO is administered to the aquatic animal via abath treatment.
 3. The method of claim 1, wherein the totalconcentration of PTS and PTSO is between at least one and no more thanfive thousand parts per million (1-5000 ppm).
 4. The method of claim 1,wherein the plurality of crustaceans is sea lice.
 5. The method of claim4, wherein the sea lice is Caligus rogercressei.
 6. The method of claim1, wherein the plurality of crustaceans has a scientific classificationof Class Maxillopoda and Subclass copepod.
 7. The method of claim 1,wherein the aquatic animal is a fish.
 8. A method for reducing parasitesin aquatic animals, comprising: administering to an aquatic animalpropyl propane thiosulfonate (PTS), the PTS having a formula R—SOa-S—R,where R represents n-propyl group (—CH₂—CH₂—CH₃) and a is 1, wherebyreducing a plurality of crustaceans infecting the aquatic animal inresponse to administering the PTS to the aquatic animal.
 9. The methodof claim 8, wherein the PTS is administered to the aquatic animal via abath treatment.
 10. The method of claim 8, wherein the concentration ofPTS is between at least one and no more than five thousand parts permillion (1-5000 ppm).
 11. The method of claim 8, wherein the pluralityof crustaceans is sea lice.
 12. The method of claim 11, wherein the sealice is Caligus rogercressei.
 13. The method of claim 8, wherein theplurality of crustaceans has a scientific classification of ClassMaxillopoda and Subclass copepod.
 14. The method of claim 8, wherein theaquatic animal is a fish.
 15. A method for reducing parasites in aquaticanimals, comprising: administering to an aquatic animal propyl propanethiosulfonate (PTSO), the PTSO having a formula R—SOa-S—R, where Rrepresents n-propyl group (—CH₂—CH₂—CH₃) and a is 2, whereby reducing aplurality of crustaceans infecting the aquatic animal in response toadministering the PTSO to the aquatic animal.
 16. The method of claim15, wherein the PTSO is administered to the aquatic animal via a bathtreatment.
 17. The method of claim 15, wherein the concentration of PTSOis between at least one and no more than five thousand parts per million(1-5000 ppm).
 18. The method of claim 15, wherein the plurality ofcrustaceans is sea lice.
 19. The method of claim 18, wherein the sealice is Caligus rogercressei.
 20. The method of claim 15, wherein theplurality of crustaceans has a scientific classification of ClassMaxillopoda and Subclass copepod.